In recent years, hybrid vehicles configured to obtain the driving force of the vehicle from a combination of a driving motor and an engine have been developed, and have increasingly found practical use. As hybrid vehicles, not only vehicles in which a generator is driven by an engine to generate electric power and a battery for supplying electric power to a driving motor is electrically charged with the generated power (PHV), but also vehicles in which the battery can be charged even by an external commercial power supply (PHEV) have been developed, and their practical use has been increased.
In some of the hybrid vehicles, an EV mode in which only the driving motor is used as a power source to drive driving wheels, a series mode in which the driving motor is used as a power source and the generator is driven by the engine to supply electric power to the battery or the driving motor, or a parallel mode in which both the engine and the driving motor are used as power sources is switched to one another depending on the traveling state of the vehicle, the charge state of the battery, or the like.
In an example of such hybrid vehicles, in accordance with the state of charge (SOC) of the battery such as a decrease in the remaining capacity of the battery during the EV travel mode, the travel mode is switched from the EV travel mode to the HV travel mode (corresponding to the above series mode or parallel mode), to actuate the engine, and the driving force of the engine is used to charge the battery or run the vehicle (see Patent Document 1).